I've run them on 3 different cars. Not as good as a fully fledged remap but worthwhile. Just make sure you get a decent one.
On my 5 series diesel and Golf R I used DTUK multi channle tuning boxes. In the BM I did 60K in it in 2 years and I thrashed the pants of that car with no issues at all. In the Golf R I ran it for 5K miles as the ECU on them hadn;t been cracked. I then took the car to stage 2 so the tuning box went.
I also bought a TMC tuning box for my s6, very good but decided I wanted to take the car further so went for a remap.
So to paraphrase the multi channel ones are very good. DTUK seem better than most but I would look at TMC for your Audi.